What is auditory processing disorder (APD)?
It is a listening or hearing disorder, which is due to the brain’s defective analysis of sounds, so that individuals who are affected with this disorder cannot make sense of what they hear.
This may manifest with many symptoms, for example, children and adults seem to be lost when they listen to someone speaking in the background of other noises such as traffic, or music.
Other difficulties can include not being able to tell where a sound is coming from, left or right, particularly if the sound is of short duration.
Some of these individuals may have problems with musical skills, picking up a melody or remembering a melody. They can have problems remembering long instructions.
They can have problems, for example, speaking on the phone, or if someone’s voice is distorted, like for example when you hear the loudspeaker announcements in the subway.
There are lots of symptoms. In addition to these symptoms, these individuals may have problems at school, or in education, or in a real-life acoustic environment, such as that of their work environment and they can have speech or language problems or other related problems.
Does APD affect adults as well as children?
Yes, it does. You may be born with APD, or you may suffer from APD because of various things that happen to you in your early life or in childhood.
But you can also acquire APD later on, because, for example, if you have a stroke or a head injury or because as we age, the same way we may lose hearing from the ear, we may lose auditory processing in the brain, so to speak.
How many people are thought to be affected by APD and what impact does it have on their lives?
Well, we don’t know the statistics, we just have a best estimate, which ranges for children between 1 to 7%, but which may well increase as you become an adult and you go into middle age and later on, because of all the acquired causes of APD.
So it’s probably a quite significant proportion but of course there may be different degrees of severity. Many individuals may cope or may learn to cope, but others may have very severe difficulties.
Children with these difficulties can face problems at school, particularly if they are still learning language and have to cope with increasing academic demands.
Sometimes these children don’t even become detected in primary or secondary, but then when they go to college, when the academic demands are even higher, they may seek help then.
And of course, when you’re an adult, you may (depending when these problems start), if you’ve had it throughout early life, have coping strategies, but then as you grow older, if you sustain any further loss in auditory processing, you can start having more difficulties and then you seek help.
Or if you sustain APD after, for example, a head injury or a stroke, and you have problems with communication with others, you may have problems with communication at work, and so on.
It depends on what exactly are the demands on your hearing. For example, if you are a musician and you suffer a stroke and this stroke affects your auditory processing, you appreciate that these patients will definitely be very, very much aware of their problem.
What is currently known about the causes of APD?
Well, we know what the risk factors associated with APD are. These can be genetic, you can be born in a family who has these kinds of problems because of defective genes.
For example, there is a gene that I’ve studied which is called PAX6, and the main manifestation is visual problems, but auditory processing problems are also very significant.
You can have other causes like, for example, prematurity and hypoxia, where you don’t get enough oxygen in the brain when you’re born, or you can have, later in life, glue ear, which goes on for a long period of time and affects how your brain matures.
You can have additional problems at any point in your life, like a head injury that affects the brain’s hearing pathways, or you can have a stroke or multiple sclerosis, which is a demyelinating disease.
Sometimes infections of the brain can affect auditory processing, but we also see another couple of categories: we see children with other types of developmental disorders, like language-related disorders or attention-deficit disorders or dyslexia.
Not everyone with these disorders, but a proportion of these individuals may have auditory processing deficits, and we don’t exactly understand whether there is a common cause for the manifestation of these different disorders or whether one is causal to the other.
Of course there is a so-called age-related APD, which is similar to the age-related hearing loss, so some deterioration of auditory processing occurs with age.
Why is APD poorly understood?
The reasons why the condition is poorly understood: firstly, because the symptoms that I talked earlier on can be part of other syndromes, like, for example, you don’t listen well if you are depressed, for example, or you don’t listen well if you’ve got attention and hyperactivity and you’re not medicated – you don’t have enough attention to keep listening, so to speak.
Or you may not listen well because English is your second language and suddenly you are in a noisy environment and it’s more difficult for you to understand what the other person is saying when they speak in English. So this is one problem.
The second problem is that at the moment there is no good standard test to say “this is happening, this is not.”
And thirdly, it’s only recently that we started having APD recognized as a disorder, and we started having discussions about what are the diagnostic criteria. And these vary in different clinics, so there is also a problem in communication between professionals at the moment.
I’m not saying that this isn’t getting better, because, for example, when I got interested in APD in 1999 and I went to the States in 2000, there was not even one clinic in the UK that was doing these tests. Great Ormond Street only started, I think, in 2001 or 2002. And there were much fewer papers in the medical literature.
But since then, the number of scientific papers that you see has exploded, interest has really exploded. There have been a lot of consensus papers in different countries, and the field is really making quite fast progress at the moment.
How is APD currently diagnosed?
The cornerstone of diagnosis is of course audiological tests. You have to test basic hearing processes, like, what’s the softest sound you can hear? Does your inner ear function well? Does your auditory nerve function well?
You also need to do more complex tests that are referred to as psychoacoustic or behavioural tests, where you present different types of sounds and the listener has to make a response and make a judgment if the sounds are the same or different, or what is the pattern of sounds, or is there a change in the sound or not.
But in addition to that you also have to get a very thorough history, and you can use questionnaires for this purpose as well, to see what exactly are the symptoms of the person and in which situations these manifest, as well as what else is happening to this person medical-wise.
You also need to consider other assessments of speech and language and of cognition or additional assessments depending on what you get on the tests and on this history.
Why does APD often go unrecognised?
Firstly, because even now in primary-care health settings, the understanding of this condition is still poor, although this is becoming better.
Again there are not too many clinics, for example, in the UK dealing with this. And again the profile of clinical set-ups is – in terms of how many you can find in which areas – is quite patchy outside the UK, it’s the same situation in the States, and even worse in Europe or in other countries.
But in addition to that, as I said, despite the fact that APD is a recognized entity in one of the formal disorder classification manuals, which is the ICD 10 of the World Health Organization, there are no agreed diagnostic criteria.
So it’s a combination of factors, it’s unrecognized amongst professionals, or sometimes they have wrong ideas about what this condition is or isn’t, and then of course access to diagnostic services can be difficult.
What can be done to improve the diagnosis of APD?
I think a lot needs to be done about coming out with standard diagnostic tests, and, for example, our own study deals with electrophysiological tests, which record the brain’s activity in response to sound, and which can help diagnosis.
In addition to new tests that need to be developed, of course one needs large-scale studies to assess individuals with these listening difficulties on a great number of tests, and to come up with valid diagnostic criteria that will be uniformly accepted.
Please can you outline the project you are working on that has been funded by children’s charity Action Medical Research? What are the main aims of this project and how do you plan to achieve them?
What we’re doing is we’re trying to assess and develop an electrophysiological test for the assessment of auditory processing disorder, and this is a test in which we’re giving different types of sounds with a headphone, and we attach electrodes on their scalp and record the brain’s response to these sounds.
These recordings can tell us where the brain activity is coming from. They can also tell us different things about basic analysis of the sounds we hear or allocating attention to these sounds.
The recordings we get and the overall brain activity helps us judge about what’s happening with the auditory processing of these sounds and the overall brain response to these, and make different judgments.
So the aim of the project is, in addition to answering different questions, which is how the auditory processing of sounds interacts with the attention and memory for the sounds, the main aim is to develop a normal diagnostic approach.
In addition to the recording of the brain’s activity we also ask the individual to tell us about their own judgment about these sounds, so we get their own behavioural response and we compare all these to other assessments of memory for sounds and attention for sounds by using validated, already existing assessments for attention and memory.
Are there any hurdles you will need to overcome?
Well hopefully we’ll get all the controls we need, because we can get APD kids from the clinic, but it’s always difficult to get normal controls because they have to spend 2 or 3 hours.
The APD families are quite motivated, because they appreciate that they need to help the research, it’s in their best interests, but normal children, they get exposed to audiology tests, so they get an experience that’s new to them and of course it’s helpful, but they need to spend some extra time, and sometimes people want to do that and sometimes not.
In terms of other hurdles we’ll need to look at of the first bit of this research and then decide how to best define the exact paradigm we’re using to make the most valid judgment for what we’re asking.
How do you think the future of APD diagnosis will develop?
Well, I think that in the years to come an additional diagnostic tool will come through imaging of the brain.
I’d be inclined to say it will be a combination of the current tests, in particular electrophysiological tests, with brain imaging techniques. The reason being that electrophysiological techniques are very good at telling us what is exactly happening at this exact point in time in response to a sound. And you appreciate that sound changes very fast.
Imaging gives us excellent information about what exactly is happening in which exact part of the brain, but it’s not so good at telling us exactly at which time.
So if you combine the two, you’ve got excellent information about both time and space, and I suspect that combined new imaging and electrophysiological studies will give us a lot more information and will help us come up with a better diagnosis.
Where can readers find more information?
I work at the Great Ormond Street Hospital and the National Hospital for Neurology and Neurosurgery where there are diagnostic services for both children and adults respectively if anyone wants to approach me regarding any clinical queries:
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